Where is the mystic key in final fantasy?

Answer 1

First you must have the submarine. Once you have it, from Junon, go underwater. head north-west. Follow the left wall, skip over the left turn into where the Gelnika crashed, then take the next left. The path will fork into 2: The first path (left) will take you to the waterfall where you meet Lucrecia, Vincent's hidden love. The second path (right), the path you will take, which seems to be just a dead end, has a secret passage at the end to the right. It's a narrow tunnel with the key at the end.